1. Field of the Invention
This invention relates to a star image sensor. More specifically, the invention relates to a sensor attached to an artificial satellite for detecting the attitude information of the satellite corresponding to a star image signal.
2. Description of the Related Art
Generally, a star sensor is used for detecting attitude information of an artificial satellite with a high accuracy to control the attitude of the satellite.
A star sensor in the related art includes an imaging device for detecting a star image and producing a star image signal to be supplied to a matching device. The matching device detects star information, such as the angular separation of stars, and compares the star information corresponding to the star image signal with memorized star information in a memory. The matching device generates an output signal corresponding to the attitude information of the satellite when the star information and the memorized star information match.
In this star sensor, the memorized star information in the memory is information corresponding to the brightness and the position of stars which were observed by a celestial telescope on the ground. Therefore, the information stored in the memory includes an error corresponding to vibrations and variations caused by the atmosphere. Also, there is a possibility that there may be no information about a dark star. In the related art, when the star information from the imaging device and the memory do not match due to the error or a lack of star information in the memory, it is difficult to detect the attitude information of the satellite with a high accuracy.
To observe a defined portion of a celestial body or a defined star in a specified direction in space, a spacecraft has to control and maintain its attitude with a high accuracy and direct an observing device in the specified direction. In such a spacecraft, information from the imaging device and the memory do not match, an improvement for detecting accurate attitude information is required.